Cartridge fuses



April 16, 1968 P. c. HITCHCOCK 3,378,659

CARTRIDGE FUSES Filed April 24, 1967 PAUL C(HITCHCOCK BY M w W ATTY.

lj' INVENTOR:

United States Patent 3,378,659 CARTRIDGE FUSES Paul C. Hitchcock, Plum Island, Mass., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Apr. 24, 1967, Ser. No. 633,081 5 Claims. (Cl. 200-132) ABSTRACT OF THE DISCLOSURE The fuse disclosed herein includes a fusible element conductively interconnecting a pair of terminal caps mounted on the outer ends of the casing of the fuse. The conductive connections between the ends of the fusible element and the terminal caps are established in a novel way by mechanical action, i.e., by pressure, rather than by solder joints.

FIELD OF INVENTION The closest prior art which is known is U.S. Patent Paul C. Hitchcock 2,691,983, Oct. 5, 1954, for One Time Fuse. The fuse structure disclosed in this patent includes means for establishing solderless connections between the ends of a fusible element and terminal caps, or ferrules, closing the ends of the casing. This is achieved by the provision of additional caps mounted on the ends of the casing outside of the conventional terminal caps, or ferrules. These additional caps have end surfaces and lateral surfaces. The latter engage under pressure the lateral surfaces of the inner terminal caps, or terminal caps proper, and press the ends of the fusible element against the lateral surfaces of the inner terminal caps, or terminal caps proper. For best results, the lateral surfaces of the additional or outer caps must be corrugated. This is a complication found to be unnecessary and undesirable. The additional caps form a separate part until held in position by the terminal caps. It is, however, more desirable to attach any fuse-element-clamping-means to the casing preparatory to closing of the casing by terminal caps, thus forming pre-fabricated sub-assemblies which include the fuse-element-clamping-means and the casing of the fuse. The structure of the above U.S. patent does not comply with this desideratum. It is, therefore, the primary object of this invention to provide cartridge fuses not requiring solder joints between the terminal caps and the ends of the fusible element, and not subject to the limitations of the structure disclosed in U.S. Patent 2,691,083.

SUMMARY OF INVENTION Fuses according to this invention include a pair of clamping inserts of sheet metal for conductively connecting the ends of the fusible element to the terminal caps closing the ends of the casing. Each clamping insert includes a tubular portion having an outer diameter substantially equal to the inner diameter of the casing, inserted into the casing at one end thereof, in coaxial relation thereto. Each of said pair of clamping inserts further includes a flange portion integral with said tubular portion thereof extending radially outwardly from said tubular portion and arranged between the end surface of one of the terminal caps of the fuse and one of the rims of the casing thereof. Each flange portion of said pair of clamping inserts is engaged and compressed radially inwardly by one ofthe pair of terminal caps. Each of the pair of clamping inserts clamps with the flange portion thereof one of the ends of the fusible element against the inner surface of one of the pair of terminal caps closing the casing of the fuse.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an exploded isometric view of one end of a fuse embodying the present invention;

3,378,659 Patented Apr. 16, 1968 FIG. 2 is a side elevation of a fuse embodying the present invention;

FIG. 3 is a longitudinal view of a portion of one end of a fuse embodying the present invention and illustrates an early manufacturing process step; and

FIG. 4 is a view similar to that of FIG. 3 and illustrates a subsequent manufacturing process step.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION In the drawings reference numeral 1 has been applied to indicate a tubular casing of insulating material having a predetermined inner diameter ID. A pair of terminal caps 2 is mounted upon the outer ends of easing 1. Each of caps 2 has a lateral cylindrical surface 2a and a flat end surface 2b. Fusible element 3 in the form of a multiperforated ribbon interconnects conductively both caps 2. How this is achieved will be explained below more in detail. Fusible element 3 is bent at three points at each end thereof. At one bent an obtuse angle or is enclosed between the central portion of fusible element 3 and section 30 thereof. At the next bent an obtuse angle 5 is enclosed by sections 3b and 3c of element 3, and at the next bent an angle deg. is enclosed by sections 3a and 3b of element 3. Fusible element 3 ends in connector tabs 3a extending in the direction of the axis of casing 1. A clamping insert 4 of sheet metal is inserted into each of the open ends of casing 1. Clamping inserts 4 comprise a tubular portion 411 having an outer diameter substantially equal to the inner diameter ID of casing 1. The tubular portions 411 of clamping inserts 4 are inserted into casing 1 at the ends thereof and are thus arranged in substantially coaxial relations to casing 1. Each clamping insert 4 further comprises a flange portion 4b integral with the aforementioned tubular portion 4a thereof and extending radially outwardly from the tubular portion. Each flange portion 4b is arranged between the end surface 2b of one of the pair of terminal caps 2 and one of the rims 1a of casing 1. Each flange portion 4b of each of said pair of clamping inserts 4 is engaged and compressed radially inwardly by the lateral cylindrical surface 2a of one of caps 2. The ends or connector tabs 3a of fuse link 3 are firmly clamped between flange portions 4b of clamping inserts 4 and the inner lateral surface 2a of caps 2. The sections 3b of fuse link 3 immediately adjacent connector tabs 3a extend parallel to the end surfaces 2a of terminal caps 2. The sections 30 of fuse link 3 immediately adjacent sections 3b are inclined relative to end surfaces 2a of terminal caps 2. The perforated center portion of fuse link 3 extends parallel to the axis of casing 1, and is substantially co-extensive with the axis of casing 1. Its length is slightly less than that of easing 1. The bents between the center portion of fuse link 3 and sections 30 thereof impart substantial flexibility to the fuse link 3, making it possible for the center portion of the fuse link 3 to expand and contract, as the case may be, without occurrence of any significant stresses and strains.

The flange portions 4b of clamping inserts 4 are preferably slightly convex at the side thereof immediately adjacent to the end surfaces 2b of the cap 2 immediately adjacent thereto.

FIG. 3 shows one clamping insert 4 whose tubular portion 4a has been inserted into one end of casing 1. It is apparent from FIG. 3 that outer diameter of flange portion 4b exceeds the outer diameter of casing 1. In other words, flange portion 4b projects radially outwardly beyond the rim 1a of casing 1. FIG. 3 shows a portion of a bending tool 5 used to compress flange portion 4b radially inwardly, thus causing flange portion 4b of clamping insert 4 to assume the shape shown in FIG. 4. After being formed by tool 5 there is still a small clearance X between the bent outer rim of clamping insert 4 and the outer surface of casing 1. This clearance X is an indication that the resiliency of portion 4b in response to radial inward pressures has not been drastically reduced, as would be the case if the periphery of portion 4b were in physical engagement with casing 1.

Upon insertion of clamping inserts 4 into casing 1 and deformation thereof by means of outwardly flaring tool 5, as described in connection with FIG. 3, fusible element 3 is inserted into casing 1. Connector tabs 3a then engage the periphery of flange portions 4b of clamping inserts 4. Thereafter one of caps 2 is mounted on casing 2 as indicated in FIG. 4. This results in clamping of connector tab St: between the outer periphery of flange portion 4b of clamping insert 4 and the inside of the lateral surface 2a of one of caps Z.

Thereafter the position of easing 1 is reversed, i.e., the structure is turned 90 degrees upside down so that its closed end is situated below and its open end is situated above. In that position casing 1 is filled with a pulverulent arc-quenching filler and then closed by mounting a cap 2 on it in the same way described above in connection with FIG. 4.

The clearance between the periphery of outer flange portion 4b of each clamping insert 4 and the outer surface of casing 1 When caps 2 are mounted on casing 1 is less than the clearance X indicated in FIG. 4. This is a result of the fact that fuse link 3 is clamped under considerable pressure by caps 2 against the flange portions 4b of clamping inserts 4, compressing flange portions 4b to some extent. The fact that link 4 is inserted between cap 2 and flange portion 4b of clamping insert 4 at one predetermined point of the periphery of flange portion 412 results in exertion of a transverse force upon cap 2 in a direction toward connector tab 3a of fuse link 3. The vector of this force has been indicated in FIGS. 1 and 2 by arrows R. The forces R establish firm frictional engagement between caps 2 and the sides of casing 2 opposite connector tabs 3a. The friction between caps 2 and casing 1 is suflicient to firmly secure caps 2 to casing 1, but not suflicient to withstand high internal pressures, as may occur on blowing of the fuse under severe fault current conditions. Hence it is necessary to crimp the axially inner edges of caps 2 into the casing 1 as widely practiced in the fuse art.

It will be understood that I have illustrated and described a preferred embodiment of the invention and that various alterations may be made in the details thereof without departing from the spirit and scope of the invention as defined in the appended claims.

I claim as my invention:

1. An electric cartridge fuse comprising:

(a) a tubular casing of insulating material having a predetermined inner diameter;

(b) a pair of terminal caps mounted upon the outer ends of said casing, each of said pair of terminal caps having a lateral cylindrical surface and a flat end surface;

() a fusible element conductively interconnecting said pair of terminal caps; and- (d) a pair of clamping inserts of sheet metal for con- 4 ductively connecting said ends of said fusible element to said pair of terminal caps, each of said clamping inserts including a tubular portion having "an outer diameter substantially equal to said inner diameter of said casing and inserted into said casing at one of the ends thereof in substantially coaxial relation thereto, and each of said pair of clamping inserts further including a flange portion integral with said tubular portion thereof extending radially outwardly from said tubular portion and arranged between said end surface of one of said pair of terminal caps and one of the rims of said casing, each said flange portion of said pair of clamping inserts being engaged and compressed radially inwardly by one of said pair of terminal caps, and each of said pair of clamping inserts clamping with said flange portion thereof one of the ends of said fusible element against the inside of said lateral cylindrical surface of one of said pair of terminal caps.

2. An electric cartridge fuse as specified in claim 1 wherein said flange portion of each of said pair of clamping inserts is convex at the side thereof immediately adjacent to the end surface of one of said pair of terminal caps immediately adjacent thereto.

3. A fuse as specified in claim 1 wherein the periphery of said flange portion of each of said pair of clamping inserts is bent to be juxtaposed to the outer surface of said casing and slightly spaced from said outer surface.

4. A fuse as specified in claim 1 wherein said fusible element extends substantially axially within said casing and has a central portion shorter than the length of said casing, said fusible element further having a first pair of obtuse angle bents each at one end of said central portion and each spaced from said flat end surface of one of said pair of terminal caps, and said fusible element further ahving a second pair of bents each around one of said flange portions of one of said pair of clamping inserts.

5. An electric cartridge fuse as specified in claim 1 wherein the outer diameter of said flange portion of each of said pair of clamping inserts exceeds in the uncompressed state thereof the outer diameter of said casing and wherein the initial spacing between the outer periphery of said flange portion of each of said pair of clamping inserts and the outer surface of said casing is reduced by pressure exerted radially inwardly by said lateral cylindrical surface of one of said pair of terminal caps upon said fusible element and upon said flange portion of each of said pair of clamping inserts.

References Cited UNITED STATES PATENTS 1,663,179 3/1928 Roth 200 131 2,173,200 9/ 1939 Grunewald 20013-2 XR 2,343,224 2/1944 Powell 200-481 XR BERNARD A. GILHEANY, Primary Examiner. H. B. GILSON, Assistant Examiner. 

